Typically theatrical lighting fixtures are intended to be fixed in position. However because of their compact size, often a theatrical lighting fixture is used as an improvised spotlight, or follow-spot. Theatrical lighting fixtures are provided with a number of controls for varying the intensity of light output and the size of the light beam. Theatrical lighting fixtures are mounted on a yoke, which allows an operator to direct the light beam up or down and from side to side when used as a spotlight. Theatrical lighting fixtures also have an iris which may be used to increase or decrease the size of the diameter of the light beam. Additionally, theatrical lighting fixtures may have a douser for varying the intensity of the light beam or blocking the light beam entirely. Often, an operator must control these several attributes of a light beam at the same time.
Among these attributes, an operator may be required to vary the position of the light beam, vary the intensity of the light beam, and the size of the light beam simultaneously. Currently, when a theatrical lighting fixture is used as a spotlight, the operator must maintain the position of the light with one hand, leaving the other hand to operate both the iris and the douser, among other functions.
When the lighting fixture is used in a side-lighting capacity, the lighting fixture is operated from the side of the stage, typically above and close to the edge of the proscenium opening. It is possible that in operation, the light will swing through an arc of 70 degrees, while shifting its throw, the distance to the illuminated subject, from approximately 20 to 60 feet. Adjusting the iris continuously and smoothly through this swing is difficult, and may be additionally challenging if there are obstructions that prevent reaching continuously. Conventional theatrical lighting equipment, and in particular the Source Four manufactured by ETC and other ellipsoidal reflector type lighting fixtures equipped with irises, are often used in this application as compact spotlights owing to their small size, allowing the lighting fixture and operator to be placed in a very small space on the proscenium of a stage set. As there are many other devices that also have to be placed on the proscenium of the stage set, space is at a premium, and many obstructions are present.
It is usually left to the operator to devise some method of marking the settings of the iris and douser, either by memory or with small pieces of tape or wire, to form a tactile indicator, as the iris is not usually in the operator's line of sight while operating the light.
Conventional theatrical lighting fixtures are also prone to light leaks, which are made more apparent when the lighting fixture is used as a spotlight. This is because lighting fixtures of this type are generally not designed to function as a spotlight, and therefore light leakage is not likely a primary design consideration. The iris slot must not be obstructed in order to allow unencumbered movement of the iris handle, but light reflects off the internal components of the lighting fixture, leading to light leaks thru the iris slot. When used as intended, the lighting fixture is equipped with a metal cover which is slid over the iris slot. This serves to stop light leafs as well as lock, through friction, the iris. Locking the iris is not always a desirable feature in a spotlight.
Light leakage from a lighting fixture may be manifested by the projection of errant rays of light to on the set in unintended and distracting patterns. The iris slot, thru which the iris handle moves, is a particularly difficult source of light leaks, as the slot cannot be covered with any of the traditional tapes or foils available to the industry, since the iris handle has to be free to move unencumbered through this slot, and additionally, the iris handle must be accessible to the operator's hand at all times.